The field of photocrosslinkable polymers has been widely studied and is of broad current interest. These polymers are used in the preparation of photoresists for use in macro- and microlithography, chemically-resistant coatings, and in the field of non-liner optical (NLO) materials.
A classical photosensitive moiety is the cinnamate group, which has the formula (C.sub.6 H.sub.5)HC.dbd.C(H)CO.sub.2 --. This moiety has been well-studied and widely used in photocrosslinkable polymers because its high sensitivity to UV radiation and the chemical resistance of the resultant polymers.
The cinnamate group crosslinks in a controlled 2+2 photo-induced cycloaddition. It is one crosslinking unit used in polymers for offset printing plates and microcomponents. Polymeric materials that incorporate the cinnamate group have existed since 1948. Minsk, L. M. et al, U.S. Pat. No. 2,690,966; Minsk, L. M., et al., J. Appl. Polym. Sci. 1959, 11, 302. The synthetic route to poly(vinyl cinnamate), in which poly(vinyl alcohol) is esterified with cinnamoyl chloride, serves as a model for the synthesis of a wide variety of photopolymers. Cinnamate containing photopolymers that have acrylate and other vinyl backbones have also been synthesized. Minsk, et al., U.S. Pat. No. 2,690,966; Minsk, L. M. et al., J. Appl. Polym. Sci. 1959, 11, 302; Nishikubo, T. et al., Makrol. Chem. Rapid. Commun. 1982, 3, 377; Mercier, R. et al., Eur. Polym. J. 1988, 24, 639; Keller, P. Chem. Mater. 1990, 2, 3; Coqueret, X. et al. Makromol. Chem. 1991, 1517.
Another photosensitive unit is the chalcone group, which has the formula --(C.sub.6 H.sub.4)--CH.dbd.CHC(O)--(C.sub.6 H.sub.5). Chalcones are particularly useful in the preparation of photocrosslinkable polymers because of the high overall photosensitivity of the chalcone unit, which is a result of the close match between the absorption spectrum of the chalcone side group and the emission spectrum of a mercury arc UV light source. This close spectral match allows for high photocrosslinking efficiency without the use of an added sensitizer.
Polymeric materials that contain chalcone-type groups have existed since 1959. These species include macromolecules with chalcone-type groups in the side chain (see, for example, Unruh, C. C. J. Appl. Polym. Sci. 1959, 6, 358; Akelah, A., et al., Polym. Int. 1992, 28, 307; Unruh, C. C. J. Polym. Sci. PtA-1 1960, 45, 325; Watanabe, S., et al., Polym. Sci. Pt. A. Polym. Chem. 1986, 24, 1227; Watanabe, S., et al. , Polym. Sci. Polym. Chem. 1984, 22, 2801; Kato, M., et al., M. J. Polym. Sci. Pt. A-1 1971, 9, 2109; Panda, S. P. J. Appl. Polym. Sci. 1974, 18, 2317; Hatanaka, H., et al., M. Makromol. Chem. 1975, 176, 3231; Panda, S. P., Sadafule, P.S. J. Appl. Polym. Sci. 1979, 24, 511; Panda, S. P. Indian J. Technol. 1976, 14, 444; and Panda, S. P. J. Armament Stud. 1975, 11, 30), in the main chain, (see, for example, Malm, B. Makromol. Chem. 1981, 182, 1307; Panda, S. P. Inst. Armament Technol. 1973, 11, 356; Davidson, R. S., Lowe, C. Eur. Polym. J. 1989, 25, 159; Malm, B., Lindberg, J. J. Makromol. Chem. 1981, 182, 2747; Rusu, G. I., Oleinek, H., Zugravescu, I. Makromol. Chem. 1974, 175, 1651; and Chem. Abstr. 1974, 82, 17595p.) and in epoxy resins (See, for example, Panda, S. P., J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 1757; Davidson, R. S., Lowe, C. Eur. Polym. J. 1989, 25, 167; Davison, R. S., Lowe, C. Eur. Polym. J. 1989, 25, 159; Panda, S. P. Indian J. Technol. 1971, 9, 387) Due to the solubility difficulties arising from the rigid-rod nature of main-chain-containing chalcone polymers, a recent emphasis has been on polymers with side chain chalcone units.
Polyphosphazenes are a class of polymers which have been reported to exhibit a number of interesting properties. The photochemical behavior and stability of poly(aryloxyphosphazenes) have been described previously. See, for example, Allcock, et al., Macromol., 1979, 12, 108; and Gleria et al., Macromol., 1987, 20, 1766. While the phosphazene backbone has been used in the field of UV-crosslinkable materials (see, for example, Gleria, M. et al., J. Inorg. Organomet. Polym. 1992, 2, 329; Gleria, M., Eur. Polym. J. 1989, 25, 1039; Gleria, M. et al. Polym. Degrad. Stab. 1988, 22, 125; Nelson, C. J.; Coggio, W. D.; Allcock, H. R. Chem. Mater. 1991, 3, 786; O'Brien, J. P.; Ferrar, W. T.; and Allcock, H. R. Macromolecules 1979, 12, 108), the use of a polyphosphazene backbone as a platform for photocrosslinkable cinnamate side groups has not been reported.
The phosphazene skeletal system has several advantages that could be exploited for photopolymer applications. These include: (1) the number of potential cross-linkable groups per repeat unit; (2) the ability to incorporate a wide variety of cosubstituents via macromolecular substitution in polyphosphazenes, which allows properties such as the glass transition temperature, solubility, lipophilicity, and biocompatibility to be tailored at will; and (3) the absence of an absorption of the polyphosphazene backbone in the mid-UV to the near infrared region, which minimizes photoinduced reactions of the skeletal system during the UV irradiation required for the photocrosslinking procedure.
Examples of known poly(organophosphazenes), and methods for their synthesis include those described in U.S. Pat. No. 4,278,660 (which discloses that square planar platinum complexes that are useful as chemotherapeutic agents can be rendered less toxic by administration in combination with a polyphosphazene), U.S. Pat. No. 4,440,921 (which discloses that biologically active molecules containing a carboxylic acid residue can be covalently attached to a polyphosphazene via condensation with a pendant amino group on the polyphosphazene), U.S. Pat. No. 4,451,647 (which teaches that heparin can be attached to an organophosphazene polymer without disrupting the polymer backbone via complexation with a quaternary ammonium ion covalently attached to the polyphosphazene backbone), U.S. Pat. No. 4,880,622 (which discloses novel poly(organophosphazene) polymers that are useful for the controlled delivery of pharmaceuticals, pesticides, herbicides, plant growth regulators, and fertilizers), U.S. Pat. No. 5,053,451 (which discloses that poly(carboxylatophenoxy)phosphazene can be ionically crosslinked to form a hydrogel), and U.S. Pat. No. 5,149,543 (which discloses a composition that includes a biological material such as a liposome, virus, procaryotic cell, or eucaryotic cell encapsulated in an ionically crosslinked polyphosphazene or other polyelectrolyte).
In light of the established utility of cinnamates and chalcones as photosensitive units, as well as the diverse properties of polyphosphazenes, it would be of interest for a variety of applications to provide cinnamate and chalcone-bearing phosphazenes, and in particular, polymeric phosphazenes.
It is therefore an object of the present invention to provide both small molecule model cyclic trimers and high polymeric phosphazenes that bear chalcone or cinnamate containing pendant groups.